The invention relates to a device for manufacturing containers from a plastics material which can be formed by stretch-blowing, with a mould, the internal space of which corresponds to the finished container, which is held by its open end by a receiving portion, wherein lines connected to a metering unit are provided on the receiving portion, a moveable stretching die is guided through the receiving portion, and an ignition means is arranged in order to ignite an explosive gas mixture inside the container, and wherein heating and cooling means are provided.
A device of the type described hereinabove for manufacturing plastics containers, for example bottles from polyethylene terephthalate (PET) is known from international published document number WO98/06559. These PET bottles are manufactured in that firstly a blank is heated to a temperature suitable for stretch blowing, of approximately 100-120xc2x0 C. This blank is inserted into a tooling mould corresponding to the shape of the container, and a stretching pressure of at least 2 bar, normally of 5-10 bar, is produced. With the aid of an axially, and in general vertically, moveable stretching die, the blank is stretched axially. Then, a blowing pressure is produced in the blank, which is in the region of 40 bar. In this way the wall of the blank is pressed against the inside wall of the mould, and in this way the container is formed. While the stretching pressure is created by blowing an explosive gas mixture into the blank, for example a mixture of oxyhydrogen gas and an inert gas, the blowing pressure is created by igniting the explosive gas mixture, and this blowing pressure presses the wall of the intermediate form, or respectively the partly pre-formed container, completely against the inside wall of the mould. In this way the PET bottle is produced. The ignition of the explosive gas mixture is done by a spark generator or an emission, and the explosive gas mixture is a mixture of an oxidising agent and a component which can be oxidised such as, for example, hydrogen, methane or the like. In the same process of stretching and blowing, by achieving a brief increase in temperature, sterilisation of the container to be manufactured is possible, so this technique is considered very advantageous.
It has been shown, however, that when converted to technology, the containers manufactured with the known device could not be used industrially. They could not be manufactured and were not reproducible with sufficient quality with respect to shape and volume, and also with respect to their optical appearance. It was for example, not possible to manufacture PET bottles with clearly transparent walls. To the extent that it was not caused intentionally or could be accounted for specific reasons, it was thought that this sometimes unattractive appearance was due to unavoidable effects of temperature.
The object of the invention is thus to provide a device of the type described in the introduction, with the aid of which plastics containers with a better appearance, for example with largely clearly transparent walls, can be manufactured without large additional expenditure.
This object is solved in accordance with the invention in that, on its end facing the container, the receiving portion can be engaged in a flowable medium-tight manner with a distribution module, through which module the stretching die is moveably guided in the axial direction, extending the receiving portion, and on which at least one connector for flowable media is fitted, in that the at least one connector for flowable media can be closed for sealing the device-side interior space, and in that ignition means is fitted in the device-side interior space. During the manufacturing process, the receiver is, in one stage, in sealed engagement with the distributor module, and in the other stage is disengaged from the distributor module. In the stretching stage, the stretching die is moveably guided through the distributor module and thereby also axially through the receiving portion.
In the case of one embodiment of the invention, a device-side interior space is formed by the parts of the device fitted together, these being the distributor module, receiving portion and the container located in the mould. With this embodiment, a flowable medium is conducted through the at least one connector for flowable media into the distributor module, and through this into the receiving portion and the container.
With another embodiment, the device-side interior space is formed by the same parts of the device, wherein, however, in addition flowable medium can also be supplied through the stretching die to the inside of the container.
In the case of a further embodiment, the device-side interior space is formed only by the container and the receiving portion arranged upon it, when, for example, the distributor module is separated from the receiving portion and the receiving portion is closed. The stretching die is conducted axially through the receiving portion, and said stretching die can include a supply line. It can, however, also be configured to be solid.
Each of the different device-side interior spaces (according to the embodiment) can be closed off in the area of the single connector for flowable media or the plurality of connectors for flowable media. Only in a closed device-side interior space does the explosion caused by the ignition means arranged externally thereto produce the desired parameters of a brief high pressure and increased temperature. Clearly, this interior space can be opened up again after the termination of the manufacturing process.
The advantage of the limited device-side interior space is its small volume. The volume in the container to be manufactured is then less critical. The container, and also preferably the receiving portion supporting it, are namely removed from the device after the respective manufacturing process, in order to be subjected to further processing. The device-side volume which was involved in enclosing the space for the explosion is, by means of the measures according to the invention, so small in relationship to the known device that reaction products, for example water when oxyhydrogen gas is used, remain in significantly smaller quantities. It has been established that the clouding of the container walls occurs because when oxyhydrogen gas is used, water formed in droplets is propelled with considerable kinetic energy from the inside onto the walls and there causes changes to the surface which in the end lead to clouding. With the first explosion, and also in the case of a continuous process for manufacturing only three to six containers, sufficient reaction product was still not formed in the device-side interior space, for example the supply and drainage lines, so there were hardly any water droplets present to cloud the internal walls of the container. With a longer continuous manufacturing process, because of the large number of successive explosions over time, there was, however, a large enough amount of reaction product (water) such that with each following explosion clouding of the container walls was unavoidable.
The closing off of a small device-side interior space, which is formed only from the interior space of the distributor module, the receiving portion and the container itself, in particular does not allow any accumulation of the unwanted reaction product (water), in that at least container itself, and preferably from the container and receiving portion is removed after the explosion, and thereby the accumulated reaction product as well. Insignificant amounts of reaction product therefore remain in the remaining device-side interior space which, even in a continuous manufacturing process, can still be ignored after a long period.
By means of this change in the construction technique of the device, it is unexpectedly possible to manufacture, without a large cost increase, plastics containers with a better appearance, in the case of PET bottles having largely clearly transparent walls.
The invention is further advantageously configured, in that the receiving portion is hollow and is provided in its end facing the container with a sealing surface through which the stretching die is conducted moveably in the axial direction extending the receiving portion. The receiving portion is preferably hollow so that the stretching die can be moved through the whole elongately configured receiving portion from one of its ends axially to its opposite end. At the same time, the receiving portion can be connected to the distributor module in a flowable medium-tight manner by means of the sealing surface which extends around the space for the stretching die, and is thus annular. It is advantageous when the stretching die is guided through this annular sealing surface in a flowable medium-tight manner so that optionally a flowable medium, preferably gases, can be forced from the distributor module through the receiving portion into the container to be manufactured, without the gases getting outside the device. By means of the hollow configuration of the receiving portion, not only can the stretching die be guided through into the container and drawn out of it again, but flowable media can also be conducted between the external surface of the stretching die and the internal surface of the receiving portion into the container, and additionally the volume inside the receiving portion is kept relatively small. In particular, the space provided for the explosion can be limited to the device-side interior space described, ensuring that chemical reactions do not place in the supply lines when reaction products occur.
It is furthermore advantageous according to the invention when the closing means for sealing off the device-side interior space is a non-return valve. Non-return valves are known per se in many various configurations. A non-return valve can be fitted to each connector of the distributor module when the embodiment is selected in which the distributor module belongs to the device which provides the device-side interior space. Another configuration of non-return valve can also be provided in addition or alternatively on the stretching die, optionally even in the stretching die, as will be described hereinafter with reference to a preferred embodiment. The device-side interior space, in the case of an advantageous embodiment, is formed by the container to be manufactured and the receiving portion, when this assembly can, for example, be separated from the distributor module.
It is further advantageous in accordance with the invention when the stretching die is configured hollow and is provided with at least one outlet aperture arranged on a stretching die tip, at least one flowable medium inlet, and with at least one internal channel connecting them, and when preferably in the area of the outlet aperture there is fitted a non-return valve. In the case of the hollow stretching die described here, the non-return valve is thus located in the stretching die, and thereby in the area of the outlet aperture. Stretching dies for the stretch blowing process are known per se. The preheated blank is stretched with the aid of the respective stretching die in that its stretching die tip engages with the base of the blank, and pushes it away. In the case of the embodiment being considered here, it is possible to arrange an internal channel in the longitudinal direction of the stretching die such that the flowable medium can be pushed from its supply-side end to the opposite side in the direction towards the stretching die tip, and out of the outlet aperture. With this embodiment, at least one gas can be transported through the internal channel in the hollow stretching die into the space inside the container to be produced, as the flowable medium at the outlet aperture adjacent to the stretching die tip can be brought directly into the volume of the container.
With another embodiment, in addition to the flowable medium inlet with an internal channel in the hollow stretching die described, connectors for flowable media can be provided, for example, on the distributor module, so that different gases can be supplied through different lines. In this embodiment too, it is always ensured that in the supply lines no combustion, and therefore no chemical reactions, can take place when, for example, the explosive gas is ignited in the volume of the container to be manufactured.
In a preferred embodiment, before ignition of the explosive gas mixture, the non-return valve in the hollow stretching die is closed. Combustion cannot take place then in the internal channel in the hollow stretching die. Because the supply and drainage lines for the flowable medium, preferably for the gases, are closed and separated from the device-side interior space before the explosion, the volume for the chemical reaction, particularly for combustion, is entirely limited to the device-side interior space. With smaller amounts of flowable media involved in the combustion, smaller amounts of reaction products also occur, so advantageously there is little fear of damaging or affecting the internal surfaces of the container to be manufactured. In this way, the appearance of the container walls can be considerably improved. Moreover, all the advantages of the known stretch-blowing process can be made use of, including sterilisation by combustion.
It is further advantageous according to the invention when in the area of the outlet aperture an ignition means is fitted inside the hollow stretching die on the side of the non-return valve facing away from the outlet aperture, and preferably is electrically connected via cables or conductor pathways to a control unit. The ignition of the explosive mixture of flowable media can take place almost in the centre of the container to be manufactured, using such a design for the hollow stretching die. Parts of the device set further outside the container can then be disengaged or closed according to the process. The actuation of the ignition means via the cable or conductive pathway also takes place advantageously through the hollow configuration of the stretching die. The connection of the non-return valve causes no interference, but instead it is preferably selected such that the whole internal channel in the hollow stretching die can be separated by means of the non-return valve from the explosion space, namely by closing the non-return valve.
In a further advantageous configuration of the invention, the hollow stretching die, which is driven such that it is moveable in the longitudinal direction, is a steel tube with a cap-shaped stretching die tip on which the flowable medium outlet is provided as a hole structure, wherein the non-return valve is provided with a valve body movable with respect to a sealing seat fitted inside the steel tube, and preferably carrying turbulence producing means. The hollow stretching die can in practice be made from a steel tube of stainless steel, the stretching die tip of which is nevertheless provided with a cap which is exchangeable, and consequently matching the properties of the respective blanks to be formed, as during the process said cap stretches the pre-heated blank by engaging with its base. The flowable medium outlet is fitted to the cap-shaped stretching die tip, preferably in the end region of the steel tube, where the stretching die tip is connected to the steel tube by means of a screw or another fastening means. As far above this as possible on the stretching die tip, the flowable medium outlet is located. It has a hole structure. This means that at least one hole is arranged in the external wall of the tube such that the gases or other flowable media flowing through the internal channel of the hollow stretching die can exit from the steel tube through this hole or respectively through a suitable number of holes. It is also possible for the flowable medium outlet to have a different exit arrangement with regularly or irregularly distributed holes. A hole structure can also be understood as a porous body of sintered metal, ceramics or the like which can then act at the same time as non-retum protection.
A preferred embodiment of the invention uses a hollow stretching die with a non-return valve which is also arranged in the area of the stretching die tip, however at a certain distance from it which is used on the one hand for receiving the flowable medium outlet, and on the other hand for the ignition means. The non-return valve in this embodiment has a valve body which can be moved with respect to a sealing seat inside the steel tube such that in this way the non-return valve is closed. If such a stretching die is arranged with strongly vertical components, preferably completely vertically, in the device according to the invention, the valve body exerts, by means of its weight, a kind of spring tensioning downwards against the sealing seat, so without a flowable medium flowing out of the internal channel, because of its weight the valve body always falls down onto the sealing seat and thereby closes the non-return valve. Obviously, the closing of the non-return valve can also be obtained in some way by building in a spring, which is necessary in particular when there is a non-vertical arrangement of the stretching die. Ignition takes place in any case in the device-side interior space, that is to say in the upper remaining space in the steel tube adjacent to the flowable medium outlet and outside the stretching die in the volume of the container, so the gas pressure increased by the explosion additionally presses the valve body against the sealing seat and closes the non-return valve.
The valve body can preferably carry turbulence-producing means. In this way a better turbulence of the flowable media mixture is obtained when it leaves the stretching die. For example, the moveable valve body can be provided with flowable medium guides running in a spiral shape on its external surface. Alternatively, outlet holes can be bored diagonally in the stretching die in order to give the exiting flowable medium a tangential speed component.
In the steel tube of the hollow stretching die, in other embodiments or alternatively in addition to the measures in the context of the embodiments described hereinabove, means are provided for good mixing of the flowable media. Thus, Christmas-tree-shaped components provided with lateral paddles can be provided in the hollow stretching die in order to improve turbulence of the flowable media while they are being conducted through.
The cap-shaped stretching die tip can be manufactured from different materials, wherein it can be made of solid plastics, of a plastics-coated steel cap, or of ceramics. A device has also already been operated and evaluated in which the stretching die tip is composed of steel. The reason for using steel instead of plastics, and for testing it, is to avoid excessive heating, and therefore affecting of the external surface of the stretching die in continuous operation.
It is advantageous according to the invention when the receiving portion is driven moveable perpendicularly to its longitudinal central axis. In this way it is unexpectedly possible to transport away a large part of the device-side interior space, namely the space in the hollow receiving portion, after each stretching and blowing process, that is to say in particular after each combustion, together with the reaction products adhering to the walls, from the remaining stationary device, for example, the distributor module with the hollow piston. All these reaction products take no part in the subsequent process of stretching and blowing, and in particular in the chemical process of combustion. The device-side interior space, which can nevertheless be coated with reaction products, is then limited to the space in the upper stretching die and in the distributor module. When an oxyhydrogen gas is used, so little water is taken along as a reaction product to the following combustion process, that affecting of the internal container walls during and after the explosion is not a risk.
Furthermore, a preferred embodiment of the invention is characterised in that the receiving portion is widened at the end facing the distributor module to form a service space in which, preferably, a centering is placed. The respective container to be manufactured has, in the case of a PET bottle, on one long end the infilling and respectively pouring aperture in the form of a band with an external thread. In the case of the known device, the receiving portion grips around this open end of the container. Also according to the invention, the container to be manufactured is retained most practically at its open end which is preferably in the form of a band with an external thread. The filling of a sterilised container is done through this infilling and respectively pouring aperture, which can also generally be described as a closure. In order that the sterile contents does not come into contact with germ-laden surfaces externally or internally on the closure, it would be advantageous when not only the inside of the container is sterilised during the combustion process in the process according to the invention, but the upper annular edge on the end face, and if possible even the thread are sterile on the outside. If according to the teaching of the invention the receiving portion is widened at the end where the container is received, there is formed an albeit small additional volume for the gas involved in the combustion, which adjoins the surface of the external thread and sterilises it during the blowing process.
It is also preferred when in this widened service space there is fitted a centring, as then both the blank and the future container can be well centred and retained. Although the centring is an additional part, which partially fills the service space, the contact with the sterilising gases during and after the combustion is not hindered or affected by it, particularly as an edge flange additionally acts as a retainer.
It is further advantageous according to the invention when in the preferably stationary distributor module a hollow piston, driven axially moveable relative to said module, is provided, which has on its external end opposite the receiving portion an annular opposing sealing surface fitting the receiving portion. The distributor module can be also constructed in one piece, and connected in a sealing manner with a correspondingly moved receiving portion such that this connection between the receiving portion and distributor module can be terminated in a controlled manner. The termination is, however, done by means of the existing measures particularly advantageously with the hollow piston. In order to connect the distributor module to the receiving portion, and respectively to disconnect it, neither the distributor module nor the receiving portion needs to be moved axiallyxe2x80x94approximately in the direction of the hollow stretching diexe2x80x94as the hollow piston is driven axially moveably, preferably pneumatically. On its external end, the hollow piston carries an opposing scaling surface fitting the receiving portion, which surface comes into sealing engagement with the sealing surface of the receiving portion when the receiving portion is connected to the distributor module. After the blowing and sterilising process, the movement of the hollow piston is reversed, so the sealing surface is disengaged from the opposing sealing surface, and then the receiving portion can be displaced in die manner described hereinabove perpendicularly to the direction of its longitudinal axis. This displacement transportation takes place each time following a blowing-sterilising procedure in the step-wise operating manufacturing process. According to the invention, in the distributor module, for guiding the stretching die, a sealing passage can be fitted in alignment with the hollow piston. With this, the movement of the stretching die in the axial direction through the distributor module, the hollow piston hereof, the receiving portion connected thereafter, and into the container, and respectively out of these parts, takes place whether the device-side interior space remains closed off in a gas-tight manner.
According to the paths of the flowable medium through the stretching die, past it or both of these, it can be advantageous when according to the invention at least one supply and connected to the metering device, and a drainage line, is connected to the distributor module. The drainage line serves to remove the reaction products, for example of the combustion gases, and optionally flowable residues.
The supply line is connected to the metering unit, which will be described hereinafter in more detail with reference to a preferred embodiment. There can be supplied, for example, for oxyhydrogen gas, hydrogen through one supply line and a mixture of oxygen and an inert gas through another supply line. With this it is advantageous when a flowable rinsing agent is forced from a further supply line to drive the reaction products out of the drainage line.
It should be noted that pressure sensors and temperature measuring devices could be arranged at different places in the device, preferably in the area of the distributor module, but also in the hollow stretching die.
It is also clear, that the ignition means can work on different physical principles. The ignition of the mixture of media takes place electrically in the most simple case by means of a spark discharge, made for example by a spark plug which can be fitted on the stretching die or on the distributor; or by means of static discharge. Other ignition methods are conceivable, for example by beaming electromagnetic energy, in the form of a laser, high frequency or microwave pulse, or with the aid of a catalytic procedure.
Another advantageous embodiment of a metering unit provides the mixing of different flowable media directly in front of the stretching die, with directly following introduction into the blank. Particularly from the safety aspect, this represents a good compromise between the manufacturing of the mixture in a separate, explosion protected pressurised container and the metering unit described hereinabove, in which by means of metering cylinders individual flowable media and/or mixtures of flowable media are supplied to the device-side interior space.
A practical embodiment is further characterised according to the invention in that in each of the supply and drainage lines connected to the distributor module there is connected a non-return valve, and the ignition means is housed in the distributor module. The stretching die is then surrounded by the space in the distributor module, the space between the stretching die and hollow piston and that between the stretching die and receiving portion with a gap. This gap means an annular space which can be seen as a channel for flowable media and can be set out accordingly. When set out larger, larger quantities of flowable media can be pumped into the container, and vice-versa. The explosion triggered by the ignition means in the distributor module then propagates itself very rapidly into the entire space filled with flowable medium. This space is limited by the non-return valves on the lines to the distributor module.
In an advantageous further configuration of the invention the hollow piston has on its end facing the receiving portion an annular sealing seat, and the stretching die carries on its end which is moveable into the container to be manufactured a radially widened portion perpendicular to its longitudinal axis for engaging with the sealing seat. This can be ball, cone or ring-shaped or the like. In this embodiment the stretching die is solid and can be configured with a smaller diameter with the result that a greater flow channel is available for the flowable medium outside the stretching die. This encourages a rapid, brief manufacturing process. The space provided for the explosion is closed off by withdrawing the stretching die and thereby introducing the widened portion into the sealing seat without the necessity for further non-return valves, wherein then the ignition means simply has to be arranged in the area of the receiving portion.
Another radial widened portion of the stretching die is also conceivable in its central area, wherein when there it is better to describe it as a step. This widened portion can then also close off the space for the explosion by engaging with the sealing seat on the hollow piston, while the stretching die still remains in the extended stretching position. In this way, the process time can be further reduced, as the stretching die does not have to be firstly withdrawn from the container before the explosion can be triggered.
It can be advantageous when according to the invention the cooling means described in the introduction are used to separately cool the stretching die. This can indeed reach a temperature of 100xc2x0 C. or more even after several steps in the step-wise continuous operation, so the materials of the device are subjected to a high degree of stress. It is then advantageous to limit the temperature of the moveable stretching die, and this can be done well, despite repeated explosions, by providing suitable cooling means.
Although the internal channel of the hollow stretching die was previously described as a supply line, clearly the supply of the mixture can also be via the distributor module and the removal of the reaction products correspondingly via the stretching die.